This invention concerns curable organopolysiloxane compositions with good adhesion. More specifically, this invention concerns good adhering organopolysiloxane compositions which cure by an addition reaction between lower alkenyl groups bonded to silicon atoms and hydrogen atoms bonded to silicon atoms.
Various combinations of organopolysiloxane compositions which cure by the above-mentioned addition reaction are known. However, these organopolysiloxane compositions generally adhere poorly to other materials. In order to adhere these organopolysiloxanes, the adhering surface must be treated with a primer beforehand. This is disadvantageous in terms of the operation's time, labor and cost.
Although numerous organopolysiloxane compositions which are self-adhering due to a combination of silane and polysiloxanes have been proposed, they suffer shortcomings such as requiring excessively high curing temperatures; having poor adhesion to plastics and durability.
The object of this invention is to offer a good adhering organopolysiloxane which cures by an addition reaction between lower alkenyl groups bonded to silicon atoms and hydrogen atoms bonded to silicon atoms. More specifically, the object of this invention is to offer organopolysiloxane compositions which adhere very well to plastics, metals and ceramics without a prior primer treatment of the surface of the material to be bonded.
In other words, this invention is an organopolysiloxane composition consisting essentially of (a) an organopolysiloxane having at least two lower alkenyl groups bonded to silicon atoms; (b) a hydrogen-containing organopolysiloxane having at least two hydrogen atoms bonded to silicon atoms wherein there is provided from 0.5 to 2.0 silicon-bonded hydrogen atoms per alkenyl group in component (a); (c) a silane having the general formula ##STR2## wherein R.sup.1, R.sup.2, Q.sup.1, Q.sup.2 and Q.sup.3 are selected independently from the group consisting of hydrogen atoms, lower molecular weight alkyl radicals, alkenyl radicals, aryl radicals, alkoxy radicals and the partical hydrolysis products from the alkoxy radicals and, (d) an addition reaction catalyst.
The components of the organopolysiloxane compositions of this invention are commercially available materials. Component (a) has the general formula ##EQU1## wherein a has a value of 1-3 and contains at least 2 lower alkenyl groups per molecule with the remainder being unsubstituted or substituted hydrocarbon radicals. Component (a) may be linear, cyclic, branched or three dimensional. It may be a homopolymer or copolymer. The degree of polymerization of (a) must result in a viscosity of 0.01-1,000 pa.multidot.s or preferably 0.05-100 pa.multidot.s at 25.degree. C. R.sup.3 is a saturated or unsaturated monovalent hydrocarbon radical.
Examples of R.sup.3 as a lower alkenyl group are vinyl, allyl, 1-propenyl and isopropenyl. Vinyl groups are preferred.
At least 2 of these lower alkenyl groups should be present on each molecule of the organopolysiloxane. Also, at least 2 of these lower alkenyl groups should be placed as far apart as possible.
Examples of R.sup.3 other than the lower alkenyl groups are alkyl groups such as methyl, ethyl, n-propyl and butyl; aryl groups such as phenyl; analogous groups substituted with halogen atoms; and other hydrocarbon groups. A majority of R.sup.3 other than the lowr alkenyl groups should be methyl groups.
Component (b) has the general formula ##EQU2## wherein b has a value of 1-3, and contains at least 2 hydrogen atoms per molecule. Component (b) may be linear, branched, cyclic or three dimensional. It may be either a homopolymer or a copolymer. The degree of polymerization should result in a viscosity within the range 0.001-10 pa.multidot.s or preferably 0.005-5 pa.multidot.s at 25.degree. C. R.sup.4 may be hydrogen or unsubstituted or substituted hydrocarbon radicals.
The quantity of component (b) must be sufficient to give 0.5 to 2.0 silicon-bonded hydrogen atoms per lower alkenyl group in component (a). It is preferred that the quantity of component (b) be sufficient to provide 0.7-1.5 silicon-bonded hydrogen atoms. Furthermore, it should be noted that a normally cured product cannot be obtained unless the sum of the number of lower alkenyl groups bonded to silicon atoms per molecue of (a) and the number of hydrogen atoms bonded to silicon atoms per molecule of component (b) is 5 or larger.
Component (c), the silane has the general formula ##STR3## and it or its partial hydrolysis product constitutes the characteristic aspect of this invention. It is an indispensable component for imparting strong adhesiveness to the product.
Examples of R.sup.1, R.sup.2, Q.sup.1, Q.sup.2 and Q.sup.3 in the general formula are hydrogen atoms, methyl, ethyl, propyl, isopropyl, vinyl, phenyl, methoxy, ethoxy, propoxy, isopropoxy and butoxy. Some specific examples are as follows: ##STR4##
The process for producing component (c) is as follows. A dichlorodialkylsilane RR.sup.1 SiCl.sub.2 is dissolved in benzene. .beta.-diketo compounds such as acetylacetone or ethyl acetoacetate are added by dropping them into the mixture and mixing under reflux at 85.degree.-90.degree. C. The hydrochloric acid by-product is removed by acid acceptors such as triethylamine or pyridine.
The amount of component (c) useful in this invention is 0.1-10 parts by weight per 100 parts by weight of the total of components (a) and (b). If the component (c) quantity is too small, insufficient adhesiveness is imparted to the product of the invention. When component (c) is in excess, the practical significance of the component is lost and curing can also be inhibited.
With respect to the addition reaction catalyst, component (d), any catalysts effective in the addition of hydrogen atoms bonded to silicon atoms to lower alkenyl groups bonded to silicon atoms, so-called hydrosilation, may be used for this purpose. Specific examples of these catalysts are finely divided elemental platinum, finely divided platinum dispersed on carbon powder, chloroplatinic acid, coordination compounds between chloroplatinic acid and olefins, the coordination compound of chloroplatinic acid and vinylsiloxane, tetrakis(triphenylphosphine)palladium, a mixture of palladium black and triphenylphosphine or rhodium catalysts.
For purposes of this invention, component (d) is used in an amount of 0.1-200 parts by weight based on the quantity of the platinum group metal per one million parts by weight of the total of components (a) and (b).
Beside the above-mentioned indispensable components, various fillers can be combined with the composition of this invention as required. Examples of these fillers are fumed silica, hydrophobicized fumed silica, precipitated silica, hydrophobic precipitated silica, fine quartz powder, diatomaceous earth, talc, aluminum silicate, alumina, aluminum hydroxide, calcium carbonate, zinc oxide, titanium dioxide, ferric oxide, fiberglass, glass beads and glass balloons. In addition, benzotriazoles, 2-ethynylisopropanol, phenylhydrazine, and other cure-retardants; manganese carbonate, carbon black and other fire-retardants; cerium hydroxide, ferric oxide and other thermal stabilizing agents; oil resistance stabilizing agents and pigments may also be combined with the compositions of the invention. The addition of various organopolysiloxanes and silanes to the compositions of this invention for purposes other than improving adhesion is also permissible.
The curable organopolysiloxane compositions of this invention are prepared by simply mixing components (a)-(d) as well as any desired fillers and additives. It is recommended that the composition of the invention be divided into two packages for convenient storage. Any desired division is acceptable. For example, it is recommended that the composition be divided into a package of components (a), (c) and (d) and another package of (b) or a package of (a) and another package of (b), (c) and (d) for storage.
The composition of this invention cures when all the indispensable components are mixed and heated to a moderate temperature. It assumes the form of an elastomer, gel or solid upon curing. It bonds with glass, metals, plastics and ceramics when it is in contact with these materials during curing. The utilization of the composition of this invention as bonding agents, sealants, coating agents, injection agents and impregnating agents is extremely beneficial because of the strong adhesion of the composition of this invention to various base materials.
This invention will be explained with the following experimental examples. In these examples, all the parts are parts by weight. All the viscosity values reported below are values at 25.degree. C. unless otherwise indicated.